Field of the Invention
The present invention relates to a glazing unit, and to be more precise an insulating glazing unit assembled from at least three panes to be used in a window in an outer wall or as an outer wall itself, in a property.
Description of the Related Art
In countries with temperatures that vary throughout the year, and in particular in countries where there is a need for considerable heating during the winter, the primary consideration when designing glazing units has been to be able to design these such that they do not release too much heat, i.e. when the internal compartment has been heated, it is desired that the heat is not to disappear out through the windows. The focus, therefore, has principally been that the panes are primarily to insulate against heat loss, i.e. they are to reduce the emission of heat.
As glazing units have become larger, and in many cases also constitute a greater part of the outer walls, an ever-greater amount of sunshine has been absorbed by the property, which during the warm part of the year creates a need for cooling, and air conditioning units are thus installed for this. As glazing units have become ever larger, and in addition in office settings in which many people and machines that create heat are present, the need for cooling in this way increases during the warm part of the year, and many air conditioning units that have been installed are not dimensioned to be able to cope with temperatures that are above a certain limit. The requirement is often posed today that the indoor temperature is not to exceed 21° C.
In order to reduce the absorption of heat by radiation, many attempts have been made to apply a coating on the inner surface of the innermost pane, possibly in the form of a sunlight-protection film applied to the inner surface of the pane. This reduces to a certain degree the absorbed radiative heat of the sun, but is reduces principally the light absorbed. The disadvantage of such a sunlight-protection film is, however, that it reduces at the same time the possibility of seeing out to the same degree. Further, it is not possible to mount such an applied sunlight-protection film onto the internal surfaces of the panes of a hermetically sealed glazing unit, an insulating glazing unit, since the heat between the panes in such a unit accelerates the breakdown of such a film and/or causes it to become detached from the pane.
Also panes that are coated during manufacture with an oxide layer on one side of the pane in order to reduce the absorption of sunshine by radiation have been developed. Such an oxide layer may be also coloured in order to give the pane a certain hue when it is seen from a distance, which may be an effect that it is desired to achieve for properties for which the complete facade principally consists of glass. Such an oxide layer is arranged on one side of the pane, and in this case normally on the internal side of the outermost pane of glazing units that are assembled from several glass panes.
In order to increase the insulating ability of the glazing units, with respect to not only the emission of heat by radiation but also the absorption of heat by radiation, insulating panes are now normally used, with two or three panes of glass that are joined in a gastight metal frame with a gas, normally a noble gas, introduced into the compartment between the different panes of glass. For such assembled insulating glazing units, a pane with an oxide coating arranged on the side that faces inwards into the property has been selected for the pane that is facing outwards from the property. The other panes in the glazing unit generally do not have a coating.
While it is true that trials have been carried out applying an oxide layer also onto a second pane, no advantages of this have been observed. The cost for a pane with an oxide layer is higher, and it is a general opinion that several oxide layers would not give any noticeable better values with respect to the emission of heat by radiation or the absorption of heat by radiation. The effects that have been seen in such trials include that the pane has removed so much light that they have been experienced as unattractive. It is possible that the choice has been made to instead increase the thickness of the oxide layer that is applied to the inner surface of the outermost pane. It has thus been possible to choose an innermost pane of a cheaper glass, completely without coating.